Th400 rebuilt

[Jusmc2006]

I live in the DFW metroplex, and I just purchased an 1986 m1009, which was driving when I received it but now the transmission seems to be out. Does anybody know of any places in the DFW metroplex, that does rebuilds on these specific transmissions.

Also if I wanted to put a 4L80 in does anybody have one in the DFW area?

 

[Barrman]

Having done a TH400 to 4L80E swap in a Suburban I want to point out a few things. You need the 4L80 to be the 4 wheel drive version. You need the 4L80 to transfer case mount pedestal (it is metric sized and the TH400 part is inch sized) You need the 4L80E dipstick and tube. I would be nice to have the 4L80E diesel torque converter. It would be nice to have the 4L80E torque converter cover.

You have to have a transmission control module. 1991-1993 have one style of wiring harness while 1994 up have another. Most if not all aftermarket controllers are made for the 1994 and up version.

1991-1994 are made for the mechanical rod shift linkage. 1995 and up are made for cable shift linkage.

You will have to move the cross member back 2 inches. Basically the rear bolt holes in the frame become the front bolt holes and you can use the cross member holes as templates to drill the new rear holes.

The shift linkage will have to be lengthened 2 inches.

Having written all of that. A stock axle 3.08:1 M1009 will not work well with a 4L80E. My 3.73:1 with 35” tires and a 4L80E runs 68-69 mph at 2,000 rpm. Besides using the torque converter lock up in 3rd gear if your controller allows it. You really won’t gain much by doing the swap in a stock M1009.

Another seldom mention thing is engine braking. The TH400 does it and does it well in all 3 gears in just about all conditions. A 4L80 E won’t do it in 4th, barely in 3rd by design. The over running clutch that allows engine braking in 2nd burns up with extreme regularity. Leaving just 1st as a reliable engine braking gear. Thelse are things I learned by experience the first time I went over a pass in Colorado.

It is your truck to do as you wish with. I am just trying to pass on things I learned.